In each cell nucleus, hidden in our massive strands of human DNA, lies the secret of longevity. Or so we thought. But tiny rings of mitochondrial DNA, responsible for coding just 13 proteins, might actually hold the key.

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What we generally just call "the genome" is, technically speaking, the nuclear genome, the collection of genetic material located in the cell nucleus. Admittedly, it is responsible for 99.9% of the organic compounds that allow our bodies to function in the way they do. But the mitochondria, the cell's energy center, has a little genome all its own. It doesn't do much - it only encodes about a dozen proteins - but those select few might have just as much to do with determining life expectancy as all the rest combined.

That's what Dr. Damian Dowling of Australia's Monash University found through his work with the beetle species Callosobruchus maculatus. As he explains:

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"What we are finding is that natural variation in this diminutive genome results in a huge range of effects on metabolism, mating behavior and reproductive biology, including male fertility. At the outset of our research program, we suspected that the evolutionary significance of the mitochondria had probably been underestimated by scientists that have come before us, but even we have been continually surprised by the magnitude and ubiquity of the effects that we have uncovered. We suspect that this genome still harbours many more secrets awaiting discovery."

It appears that certain combinations of mitochondrial and nuclear genomes can produce long life in certain types of female beetles. Intriguingly, the different permutations apparently correlated with the beetle's sexual activity - one combination conferred longevity on virgin beetles, a different one gave long life to females that mated only once, and another provided it to females that mated many times. Here's hoping this isn't headed towards a nightmare scenario where people with a certain genomic combination need to choose between sex and immortality.

On a less fanciful note, Dowling hopes that the relative simplicity of the mitochondrial genome will provide an easier path towards figuring out how to slow down the aging process:

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"As we unravel this complexity, we draw closer to the day in which we might use the genetic information encoded in the mitochondria to assist in the development of therapies that slow the onset of ageing in humans.